This application is based on Japanese Patent Application 2001-009003, filed on Jan. 17, 2001, the entire contents of which are incorporated herein by reference.
A) Field of the Invention
The present invention relates to a surface emitting semiconductor laser device and its manufacture method, and more particularly to a surface emitting semiconductor laser device suitable for laser oscillation at a wavelength longer than 1 xcexcm and its manufacture method.
B) Description of the Related Art
A high gain strained quantum well layer having an oscillation wavelength of 1 xcexcm or longer and a high reflectivity semiconductor DBR mirror can be formed by using an InGaAs substrate. A surface emitting semiconductor laser device of a 1 xcexcm band has been proposed which has a strained quantum well layer of GaInNAs or GaAsSb formed on a GaAs substrate.
If InGaAs is used as a substrate material, the material of a semiconductor DBR mirror and a laser structure to be formed on the InGaAs substrate is usually ternary or quarternary compound semiconductor. If compound semiconductor made of three or more atoms, there is some fear of a high heat resistance of a laser device.
If GaAs is used as a substrate material, a highly efficient DBR mirror can be manufactured by alternately laminating a GaAs layer and an AlAs layer. However, it is difficult to improve the quality of a strained quantum well layer made of GaInNAs, GaAsSb or the like and a surface emitting semiconductor laser device having a low threshold value is not realized as yet.
It is an object of the present invention to provide a surface emitting semiconductor laser device having a high efficiency and a low thermal resistance and being suitable for laser oscillation at a wavelength of 1 xcexcm or longer and its manufacture method.
According to one aspect of the present invention, there is provided a surface emitting semiconductor laser device, comprising: a substrate made of a first semiconductor having a first lattice constant; a lower multi-layer mirror disposed on a surface of the substrate, the lower multi-layer mirror having a first layer made of a second semiconductor oxidized and a second layer made of a third semiconductor alternately stacked; a strain relaxation layer disposed on the lower multi-layer mirror and made of a fourth semiconductor having a second lattice constant different from the first lattice constant; an active layer including a luminescence region disposed on the strain relaxation layer and made of a fifth semiconductor having a third lattice constant different from the first lattice constant; and an upper multi-layer mirror disposed on the active layer.
According to another aspect of the present invention, there is provided a method of manufacturing a surface emitting semiconductor laser, comprising the steps of: forming a first lamination structure on a surface of a substrate made of a first semiconductor having a first lattice constant, the first lamination structure being made of a first layer made of a second semiconductor and a second layer made of a third semiconductor alternately stacked; growing a strain relaxation layer on the first lamination structure, the strain relaxation layer being made of a fourth semiconductor having a second lattice constant different from the first lattice constant; patterning the first lamination structure and the strain relaxation layer to expose side faces of each layer; oxidizing the first layers from side faces thereof under a condition that the first layers are oxidized and the second layers and the strain relaxation layer are not oxidized; forming an active layer on the strain relaxation layer, the active layer including a luminescence region and being made of a fifth semiconductor having a third lattice constant different from the first lattice constant; and forming an upper multi-layer on the active layer.
As the first layer is oxidized, strains in the upper strain relaxation layer are relaxed more than the strains immediately after the growth of the strain relaxation layer. By growing the active layer on the strain relaxation layer whose strains were relaxed, the quality of the active layer can be improved. By inserting the strain relaxation layer between the substrate and active layer, the selection degree of freedom of substrate materials becomes high. It is therefore possible to use binary compound semiconductor having a small heat resistance as the material of a substrate.